In numerous mechanical applications, the system generating mechanical power is remote from the receiver; on a helicopter, the tail rotor is often several meters away from the engine. The power needed to drive the rotor must be conveyed mechanically to the rotor by a so-called “transmission”; the driving torque may reach or exceed 1000 newton meters (Nm), and the speed of rotation may reach or exceed 20,000 revolutions per minute (rpm).
This distance leads to dispersions between the geometrical positions of the engine and the receiver. Dispersions in position between the engine and the receiver are the result either of manufacture, or of deformations under load caused by the system being in operation (for example the tail beam of a helicopter can deform when the tail rotor is in use).